Uncoated facestock for adhesive-backed labels

ABSTRACT

Disclosed is an uncoated facestock product having enhanced printability, holdout, and edge wick properties, which are attained through a combination of manufacturing techniques including increased refining of the furnish, sizing, increased hard nip calendering, and the use of extended nip calendering. The resulting uncoated facestock product has the following properties: a density between about 0.7 and 1.0 g/cc and/or an ash content of less than about 15% as measured by the 525° C. standard test method; and a finished surface having a Sheffield smoothness between about 50 and 150 Sheffield units and a Parker Print Surf roughness (PPS-10) less than about 5.0 microns.

FIELD OF THE INVENTION

This invention relates generally to uncoated facestock foradhesive-backed labels and a method to manufacture the same. Moreparticularly, this invention relates to a unique combination ofrefining, sizing, conventional hard-nip calendering, and extended nipcalendering of uncoated paper to obtain a material that can replacecoated one-side or coated two-side facestock (“coated facestock”)presently used to make adhesive-backed paper labels.

BACKGROUND OF THE INVENTION

There is a need in the marketplace to replace coated facestock withuncoated facestock for use in adhesive-backed labels. A driving forcebehind this need is to cut the high cost associated with the purchase,application, and handling of the coatings that are used to coat suchfacestock materials.

Requirements that must be met by an uncoated facestock before it can beused to replace certain coated facestocks include obtaining a surfacehaving good flexographic printing, adequate UV adhesive holdout, andminimum edge wick.

In order to attain the micro-smoothness required for good flexographicplate contact and ink transfer, conventional papermaking processes tendto compress the sheet, sacrificing bulk, stiffness and convertingperformance. Since facestock generally requires only one side to befinished (e.g. for subsequent printing and/or over-laminating), aprocess which could preferentially treat one surface would be desirable.

Temperature gradient calendering is a known process where the surface ofthe paper is heated to a temperature higher than the glass transitiontemperature of the cellulose in the nip while the bulk temperature ofthe sheet is substantially cooler. This process enables smoothnessdevelopment with reduced bulk loss compared to conventional hard-nip(machine calendering) or hot-soft calendering. In addition, surfacemoisturization can also be used to lower the glass transitiontemperature preferentially closer to the surface to develop smoothnesswith minimum bulk loss.

Hot-soft calendering, another method of calendering that is commonlyused for coated substrates, also relies on the temperature gradientcalendering concept, but the web that is being pressed against a hotsurface in a nip is supported by a roll that has a deformable cover.This cover gives the paper a longer dwell time in the nip compared tohard nip calendering and also allows the smoothness and glossdevelopment to occur at relatively uniform density across the width ofthe paper. Soft calendering is an expensive option for existing machinesand has limitations, such as cover delamination and cracking due tooverheating.

Extended nip calendering extends the soft calendering concept to longernip widths and reduces the operational problems. One type of extendednip calendering uses an endless band/belt over a backing roll to providesupport for a paper web that is pressed against a heated cylinder.Another variation to this concept is to use a shoe instead of a roll asa backing for the paper web. The backing shoe provides longer nipwidths, hence an increase in dwell time and a decrease in peak nippressure. Use of extended nip calendering has provided substantialbenefits for the manufacture of certain paper products such as envelopepaper (reference U.S. Pat. No. 6,332,953).

Based on the high cost of coating conventional coated facestock, thereis clearly a need in the market for uncoated facestock materials thathave suitable or improved performance in comparison to conventionalcoated facestock.

SUMMARY OF THE INVENTION

This invention relates generally to the development of an uncoatedfacestock for adhesive-backed labels, and to a method for manufacturingthe same, that may be used to replace coated facestock presently in usetoday. The invention results from discovering a unique combination ofpaper manufacturing techniques including refining, sizing, conventionalhard-nip calendering, and extended nip calendering of uncoated facestockto obtain a material that can replace coated facestock presently used inadhesive-backed labels.

In particular, the present invention is an uncoated facestock materialhaving the following properties: (1) a density between about 0.7 and 1.0g/cc and/or an ash content of less than about 15% (measured inaccordance with TAPPI Test Method T 211 om-93); and (2) a finishedsurface having a Sheffield smoothness between about 50 and 150 Sheffieldunits (measured in accordance with TAPPI Test Method T 538 om-88) and aParker Print Surf roughness less than about 5.0 microns (measured inaccordance with TAPPI Test Method T 555 om-94 using a pressure of 10kgf/cm² with a soft backing (PPS-10)).

Additional properties of import include: (3) a 1% HST value greater thanabout 50 seconds (using a 1% formic acid solution and 80% reflectance);(4) a cross-machine direction tensile strength greater than about 15lbf/inch; (5) a Gurley Stiffness of about 80 and 200 mgf as measured inthe machine direction; and (6) a Gurley Stiffness of about 40 and 200mgf as measured in the cross-machine direction (measured in accordancewith TAPPI Test Method T 543 om-94.)

A customer may utilize the uncoated facestock product described above tomake a label laminate that is useful as a name badge label, addresslabel, shipping label, or the like. A process for making such labels isas follows: (1) apply a release material layer, such as silicone, on asurface of a release liner and allow the release material to dry; (2)apply an adhesive layer on the release material layer and allow theadhesive to dry; and (3) laminate the combined release liner, releasematerial layer, and adhesive layer to the uncoated facestock so that theadhesive is in contact with the surface opposite the finished surface ofthe uncoated facestock product.

The customer (or a downstream customer of that customer) may utilize theproduct manufactured immediately above to make a dairy type label asfollows: (1) print a pattern (e.g., corporate logo, product description,product contents) onto the finished surface of the uncoated facestockcomponent of the label laminate; (2) apply a second adhesive layer tothe finished surface of the uncoated facestock over the printed pattern;and (3) laminate a film such as polypropylene over the second adhesivelayer. The resulting product may be used for dairy labels, sodacontainer labels, and the like.

In accordance with a method of manufacturing uncoated facestock, afterthe paper is dried in a main drying section of the paper machine, thepaper web is passed through a size press (e.g., puddle or meteringincluding rod or blade) where the amount of pickup can be controlled.The size-press-treated paper is dried in the after section to a moisturelevel of about 4-6%. Following the size press treatment, the paper maybe remoisturized using water showers (hydraulic, air atomized,ultrasonic) or steam showers on one or both sides of the paper. Theamount of moisture addition will be between about 0.25-6% by weight.

Following the last dryer section, the web is calendered in one or morenips of a conventional hard-nip calender stack or a hot-soft calender,and finally by an extended nip calender. The extended nip calenderincludes a heated roll against which the surface that is being smoothedis pressed using a roll-backed or shoe-backed soft belt to support theweb.

The extended-nip calender may be installed following the conventionalcalender stack/hot-soft calender, or it may be retrofitted from anexisting machine calender. Retrofitting is an economical option comparedto installing a new calender.

The heating in the belt calender rolls can be accomplished by any knownprocesses, including internal induction, hot oil circulation, externalinduction, steam heating, direct heating, infrared heating and othersuch means. The heating process is designed to maintain the surface ofthe calendering rolls at a temperature of greater than about 121 deg. C.The nipload applied in the heated nips is preferably in the range fromabout 250 to 500 kN/m for a 70 mm shoe with a nip width of about 1 to 25cm. The effective nip pressure can be reduced as the length of the shoeis increased. The preferred shoe length is about 30-100 mm.

Except for the use of an extended nip calender, uncoated facestock paperis generally made utilizing conventional paper making equipment. It isnotable, however, that a unique combination of processes have beenemployed to obtain the characteristics described herein to successfullyobtain satisfactory uncoated facestock that can replace coated one-sideor coated two-side facestock in applications involving filmoverlamination.

In brief, the combination of processes may include one or more of thefollowing techniques: (1) increased refining of the uncoated facestockfurnish; (2) increased sizing of the web in combination with the use ofpreferred sizing agents; (3) control of the temperature of the hard-nipcalendering roller(s); (4) controlled application of steam or liquidwater to the surface of the web just prior to calendering; (5)increased/additional hard-nip calendering; and (6) and extended nipcalendering. The proper combination and implementation of thesetechniques all contribute to the ultimate success in making an uncoatedfacestock having improved flexographic print qualities, good holdout,and minimal edge wicking suitable for pressure-sensitive applicationsinvolving subsequent overlamination of the printed facestock with aprotective film.

BRIEF DESCRIPTION OF THE DRAWINGS

So that those of ordinary skill in the art to which the subjectinvention pertains will more readily appreciate how to make and use theuncoated facestock disclosed herein, the paper product, its method ofmanufacture, and its use as a base product for manufacturing varioustypes of labels is described in detail herein with reference to thefollowing drawings, wherein:

FIG. 1 is a diagrammatic view of a typical arrangement of a Fourdriniermachine suitable for use in manufacturing paper.

FIG. 2 is a diagrammatic view of a representative size press andaftersize dryer section which can be used in manufacturing paper.

FIG. 3 is a diagrammatic view of a known calendering section of a papermachine which has been retrofitted to an extended nip calenderingarrangement for use in finishing facestock paper in accordance with anembodiment of the invention.

FIG. 4 is a diagrammatic view of an alternative extended nip calenderingarrangement which can be used to finish facestock paper in accordancewith an embodiment of the invention.

FIG. 5 is a diagrammatic view of an extended nip calendering arrangementin which a conformable belt is supported against a heated calender rollby means of a backing shoe arrangement for use in finishing facestockpaper in accordance with an embodiment of the invention.

FIG. 6 is a side view of a film-laminated pressure-sensitive labelproduct that incorporates uncoated facestock paper made by utilizing theunique combination of manufacturing techniques disclosed herein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention relates to a combination of steps includingrefining, sizing, conventional hard-nip calendering, and extended nipcalendering to manufacture an uncoated facestock that replaces coatedfacestock presently used in adhesive-backed labels.

The teachings of U.S. Pat. Nos. 6,332,953, 6,287,424, 6,274,001,6,190,500, 6,203,307, 6,007,921, 5,694,837, and 5,400,707 provideadditional enabling disclosure for the present invention. The contentsof these patents are incorporated by reference herein. Those of ordinaryskill in the art of paper making will appreciate the relevant teachingsfound in these prior art references.

Definitions

As used herein, the term “dairy label” refers not only to labels used oncardboard, glass, and plastic milk containers, but also to labels usedin similar applications. Such products may be manufactured by thefollowing steps: (1) silicone coating a release liner; (2) applyingpressure-sensitive adhesive to either the liner over the siliconecoating or to the non-finished side of an uncoated facestock; (3)laminating the release liner and the uncoated facestock together; (4)flexography printing the finished side of the uncoated facestock; (5)applying an adhesive (typically UV-cured) on the printed side of theuncoated facestock; and (6) over-laminating a clear film onto theprinted side of the uncoated facestock over the adhesive. The functionof such a film is often to protect the facestock, for example, fromwater of condensation for refrigerated packaging. This process will bedescribed with reference to FIG. 6 in greater detail herein below. Goodholdout of the adhesive in step 5 is important to making a quality dairylabel. To achieve adequate holdout and meet edge wick requirements, thefacestock surface region must be sufficiently non-porous and the sheetmust be sufficiently sized.

As used herein, the term “coated paper” refers to a paper product towhich at least about 8 g/m² of coating color solids have been applied toat least one surface at a coating station. Examples of common coatingstations include blade coaters, rod coaters, short dwell applicatorcoaters, gate roll coaters, film press coaters, fountain coaters, andthe like. The mixture of coating color will generally consist of: (1)pigment(s) such as clay, calcium carbonate, titanium dioxide, and thelike; (2) binder(s) such as modified starch, styrene butadiene rubber,polyvinyl acetate, vinyl acrylic, or polyvinyl alcohol; and (3) variousfunctional additives such as dispersants, viscosity modifiers,cross-linking agents, lubricants, and the like. The resulting mixture isapplied at a mixture solids content of about 40% or greater by weight,and means are provided for controlling the amount of dry coat weightapplied. A size press operation applying a starch/pigment mixture to thesheet may or may not be used prior to the coating station.

As used herein, the term “uncoated paper” refers to any paper productwhich has 0.0 to about 8 g/m² of a starch or starch/pigment mixture ofsolids applied to one or both sides of the web, but which does notundergo subsequent surface application as described above. “Uncoatedpaper” thus may or may not undergo treatment at the size press. If astarch or starch pigment mixture is applied at the size press, thesolids content of the mixture for “uncoated” paper will be less thanabout 40% by weight.

As used herein, the term “facestock” generally refers to the primarysurface material that forms the actual label of a paper label. Withrespect to the presently disclosed invention, the term “uncoatedfacestock” paper means uncoated facestock paper having the followingmaterial properties: (1) a density between about 0.7 and 1.0 g/cc,and/or an ash content of less than about 15% as measured by the 525° C.standard test method, (2) a finished surface having a Sheffieldsmoothness between about 50 and 150 Sheffield units and a Parker PrintSurf roughness (PPS-10) less than about 5.0 microns.

Additional properties may include: (3) a 1% HST (80% reflectance) valuegreater than about 50 seconds; (4) a cross-machine direction tensilestrength greater than about 15 lbf/inch; (5) a machine direction Gurleystiffness of about 80 to 200 mgf; and (6) a cross-machine directionGurley stiffness of about 40 to 200 mgf.

As used herein, the term “holdout” refers to the ability of a sheet ofpaper to resist penetration by flexographic inks and adhesive coatingsapplied to a printed or unprinted surface during manufacture of afilm-overlaminated pressure-sensitive facestock.

As used herein, the term “hard nip calender” refers to two hard-surfacedrollers whose axes of rotation are parallel and whose roller surfacesare pressed against one another so that a nip is formed there between.Paper may be passed through the nip to improve the surface finish of thepaper.

Referring to FIG. 1, facestock paper can be formed on a conventionalFourdrinier machine 2 fitted with a headbox 4. The furnish for theheadbox 4 is provided by conventional means. Headbox 4 deposits thefibers on a forming table 8 of the Fourdrinier machine. At a suitableposition along the forming table 8, vacuum is applied using conventionalsuction boxes 12. Water is removed by the foils 10 and by the suctionroll 14. The web W exits the Fourdrinier machine and enters aconventional press section (not shown), which removes additional waterby mechanical pressure. Additional process equipment may be used inconjunction with the Fourdrinier. For example, a top-former dewateringunit or a Dandy roll may be used.

It is notable that the furnish used for manufacturing uncoated facestockshould be refined to a greater extent then would normally be done with asimilar furnish that is to be used for more conventional uncoated paperproducts. Such additional refining will assist with closing up the sheet(which improves holdout) and will also enhance smoothness (whichimproves flexographid print quality). Standard mechanical refiningmeans, such as disk or conical refiners, are satisfactory for thispurpose. Those skilled in the art will appreciate that the degree towhich the furnish should be refined will greatly depend on the qualityof the refining equipment and paper making equipment, the furnish (e.g.,refining response for northern species is different than that forsouthern species), and the final specifications of the uncoatedfacestock.

Following pressing in the press section, the paper web is dried in themain dryer section (not shown) of the paper machine. Referring to FIG.2, the dried web is then optionally surface sized at a size press 16(e.g., of the puddle or metering type) where the amount of pickup can becontrolled. Sizing operations are carried out primarily to provide paperwith surface strength and control of penetration by aqueous solutions.The treatment also improves the surface characteristics and certainphysical properties of the paper such as stiffness. During surfacesizing, surface voids in the sheet may be filled with pigment and starchor other binder particles.

FIG. 2 shows a size press station 16 having an inclined configuration.However, it will be appreciated by persons skilled in the art that theuse of an inclined configuration is not necessary. In the alternative,the size press may be horizontal or vertical or have metering elementssuch as a rod or blade. In the inclined size press shown in FIG. 2, theweb W passes through the nip between a pair of opposing size press rolls18 and 20 at an angle of inclination between 0 to 90 deg., e.g., 45 deg.The nip formed by rolls 18 and 20 is flooded with sizing solutionsupplied on both sides of the web by respective banks of solution supplytubes 22 a and 22 b spaced in the cross machine direction. The web Wabsorbs some of the solution and the unabsorbed solution is removed bythe pressure in the nip. The overflow solution is collected in a pan 24arranged directly below the press rolls and is recirculated back to thenip through the solution supply tubes.

The size press 16 can be used to add a variety of agents for a varietyof purposes (e.g., starch and polyvinyl alcohol for strength, pigmentssuch as calcium carbonate and clay for improving the brightness,opacity, and smoothness of the product). The starch solution (e.g.,unmodified, acid modified, preoxidized or hydroxyethylated) may have astarch solids concentration in the range of about 1 to 25%. In addition,the size press solution may optionally contain a lubricant that iscompatible with the starch and other binders. This lubricant can belongto a class of polyethylene emulsions or can be a polyglyceride. Opticalbrighteners may also be added at the size press. The size press-treatedpaper is dried in a dryer station 26 to a moisture level of about 2 to6%.

It has been found that higher levels of sizing, as measured by theHercules Size Test (HST) test (using a 1% formic acid and an 80%reflection endpoint), benefits holdout of both ink and adhesive. Sizingusing about 5 to 18 lb/ton Cypress® 225 styrene acrylic acid sizingagent (Cytec Technology Corp., DE, USA) at the size press has provensuccessful. Sizing agents other than Cypress® 225 have worked as well aslong as sufficient sizing levels (as measured by HST) were achieved. Forexample, about 5 to 15 lb/ton of Baysize® styrene acrelate emulsion(Bayer Aktiengesellschaft, Germany) has worked well.

Following the size press station 16 and dryer station 26, the paper webW is passed through a first multi-roll calender stack 28 as shown inFIG. 3. The calender stack 28 may be equipped with one or moreconventional waterboxes 29. FIG. 3 shows a wet stack 28 having twoconventional waterboxes 29 a and 29 b which conventionally apply wateror aqueous solutions to respective sides of the paper. As described ingreater detail herein below, because the machine calendering line shownin FIG. 3 is retrofitted with moisturizing showers 30, the waterboxes 29a and 29 b are not used to apply moisture to the paper, i.e., thewaterboxes are either removed or left in place but not activated toapply liquid to the paper web. Multi-roll calender stack 28 is shown toinclude six rollers; however, the stack may include as few as tworollers. The number of rollers required will depend on, for example, howmuch calendering is needed, whether moisture is to be added to thepaper, whether moisture is to be added to one or both sides of thepaper.

After the paper web W has passed through the stack 28, the web may bemoisturized on one or both sides using one or more moisturizing showers30. The moisturizing showers may consist of water showers (e.g.,hydraulic, air atomized or ultrasonic showers), steam showers, or acombination of water showers and steam showers. In an embodiment of thepresent invention, steam showers are used to apply steam to the websurface in an amount of about 0.5 to 6 g/m².

Calender stack 34 comprises calender rolls 34 a-34 e, at least one ofwhich may be heated. In accordance with an embodiment of the invention,a soft, i.e., conformable, endless belt 36 is installed such that thebelt is partially wrapped around calender roll 34 d, which is unheated,to form a first extended nip with calender roll 34 c, which is heated,e.g., by an external induction heater 35 a. The belt 36 presses the webagainst the surface of heated calender roll 34 c and is supported by aplurality of guide rolls 39 and by calender roll 34 d. Although FIG. 3shows belt calendering of the wire side of the web, alternativearrangements can be used to calender the felt side instead. For example,the felt side can be calendered by wrapping the belt around calenderroll 34 c and then heating calender roll 34 b instead of calender roll34 c.

In accordance with the embodiment shown in FIG. 3, the calendered sideof the web W can be moisturized using a moisturizing shower 30 f, e.g.,steam shower. In addition to moisturization, the steam shower will alsoraise the temperature of the surface of the calendered side of the web.The moisturized side of web W is then smoothed as it passes through thehot extended nip formed by heated calender roll 34 c and conformablebelt 36. The steam shower 30 f is located very close to the firstextended nip between rolls 34 b and 34 c so that the time intervalbetween steam application and hot extended nip calendering is minimized.Minimizing this time will preserve a gradient in moisture across thethickness of the web.

In cases where more than one moisturizing shower is used to applymoisture to the same side, the last shower that applies moisture shouldbe located as close to the extended nip as possible. The dwell timebetween moisturization using the steam shower 30 f and calendering inthe first hot extended nip should be about 0.01 to 6.0 sec. The niploadin the heated nip between rolls 34 c and 34 d is preferably in the rangefrom 250 to 500 kN/m (for a nip width in the range of 1 to 25 cm).

Preferably, calender roll 34 b is adjusted against calender roll 34 c sothat the finished side of the web will be hard nip calendered beforeentering the first extended nip calender. Greater use of machinecalendering prior to extended nip calendering has shown reducedpermeability in the uncoated facestock and improved adhesive holdoutprior to over-laminating with polypropylene films. In addition, it hasbeen found that additional calendering also decreases stiffness, andimproves Sheffield smoothness, and reduces Parker Print Surf roughness.

It is notable that in contrast to the manufacture of envelope paperproducts that preferably minimizes bulk reduction (ref. U.S. Pat. No.6,332,953, col. 1, lns. 10-14, and col. 2, lns. 59-65), the minimizationof bulk reduction is not particularly critical in the manufacture ofuncoated facestock. Therefore, machine calendering may be more readilyutilized to fine-tune the surface finish of uncoated facestock asdescribed above.

As depicted in FIG. 3, optionally calender roll 34 e may also be heated,e.g., by external induction heater 35 b, to provide a second hotextended nip for further smoothing of the calendered side of the web W.In such case, the web can be remoisturized by moisturizing shower 30 gbefore the web enters the second extended nip formed by heated calenderroll 34 e and conformable belt 36.

In accordance with an embodiment of the invention, calender rolls 34 cand 34 e may be heated by conventional external induction heater 35 aand 35 b, respectively. However, it will be appreciated by personsskilled in the art that other conventional means could be used to heatcalender rolls 34 c and 34 e. For example, the hot pressure nips can becreated by heating one or more of the rolls in stack 34 using internalsteam, circulating oil or other heating fluid, internal or externalinduction coils, direct heating or infrared heating. The heat input intothe rolls is preferably sufficient to maintain a roll surfacetemperature of greater than about 121 deg. C. (250 deg. F.) duringcalendering of the web.

Although the calendering line shown in FIG. 3 comprises two calenderstacks 28 and 34 separated by intercalender dryers 32 a-32 d, it shouldbe appreciated that to finish the uncoated facestock paper requires, ata minimum, only a single calender stack including, for example, one nipof a hard nip calender. Subsequent calendering using an extended nipcalender is preferred but not always necessary.

When intercalender dryers are present, they are normally used to dry thesheet to lower the moisture that the web picks up in the wet stack. Thisdrying is not needed because, as noted above, the waterboxes on the wetstack are not used. Therefore, the intercalender dryers can be used tocool the sheet by running cold water or other cooling fluid throughthem. Alternatively, the web may be routed around any of the existingintercalender dryers simply to extend the convective cooling during webtravel. In such case, the dryers need not be filled with a coolingmedium.

In a dry stack 34 retrofitted with an endless conformable belt 36, thebelt 36 is formed using a fabric base and coated using a polymericmaterial such as a polyurethane. The belt 36 is pre-formed in that it issupplied as a continuous loop. The finished belt 36 may have a hardnessfrom 58 Shore A to 88 Shore C and a thickness of 5-25 mm, and isfinished to a surface roughness of no greater than 8 μm RMS.

In addition, the uniformity of the belt 36 will be such that thethickness variation across the width of the paper machine will be nogreater than 0.02 mm. The loop length of belt 36 will be optimized to belocated in the available space in the dry stack and also have sufficientcooling outside the nip. Installation of the endless belt 36 on thecalender stack may be an involved procedure. As an alternative to usingan endless belt, the belt can be seamed in place and the seam coveredwith a material that minimizes marking due to the seam in thecalendering operation.

To practice the invention it is possible to retrofit a conventionalmachine calendering section by installing a conformable belt. Inaddition, the conventional machine calendering section may beretrofitted with moisturizing showers and external induction heaters, asshown in FIG. 3.

In accordance with a further alternative, the uncoated facestock may bemanufactured by installing a belt calendering arrangement of the typeshown in FIG. 4 in place of the dry stack. The belt properties used in anew calender installed in place of an existing dry stack will be similarto the properties described for the retrofitted calenders. Coolingdevices other than intercalender dryers, such as cooling cylinders,chill boxes, chill rolls and air showers, can be used to cool the sideof the paper which is not contacted by the heated calender roll of thebelt calendering arrangement. Use of such cooling devices is optional.

Referring to FIG. 4, the tension in the web W can be adjusted bychanging the position of a tensioning roll 38 utilizing any conventionaltensioning device (not shown). The web is wrapped partly around a guideroll 40 and passes through an extended nip formed by a heated calenderroll 42 and a conformable belt 44 made of resilient material.

The position of guide roll 40 is adjustable to increase the angle ofcontact of the web W with the heated calender roll 42 upstream of theextended nip, which angle of contact determines the amount of preheatingapplied to the web by the heated calender roll 42. Before entering thenip, the web W is optionally moisturized by a bank of moisturizingshowers 41 of the type previously described. The web W is pressedagainst the heated calender roll 42 by a backing roll 46 that exerts aload on the belt 44.

Belt 44, which may be either endless or seamed, circulates on carrierrolls 48 and 50 and tensioning roll 52. The tensioning roll 52 isrotatably mounted on the end of a pivotable arm 54. A guide roll 56 islocated outside and in contact with belt 44. The backing roll 46 isrotatably mounted on a loading arm 58, which is in turn pivotablymounted on a support frame 60. The loading arm 58 has a first angularposition (shown in FIG. 4) in which the backing roll 46 presses the belt44 against the heated calender roll 42, and a second angular position(not shown in FIG. 4) in which the belt 44 is relaxed and separated fromthe heated calender roll 42 by a gap.

The surface of the heated calender roll 42, when pressed against theside of the web W that will be printed, applies heat. The residence timeof the web in the extended nip is sufficiently short so that the heatdoes not penetrate through the entire thickness of the web. The appliedheat raises the surface temperature of the paper to the glass transitiontemperature or higher, which causes the fibers to soften and conformunder pressure to the surface of the heated calender roll 42. Thisallows the treated surface of the web to achieve desired smoothness anddesired printing performance at an improved level of adhesive holdoutfor subsequent film overlaminating.

The calendered web passes under guide rolls 62 and 62′ and then overguide roll 64. A scanning sensor unit 66 measures the moisture level andbasis weight of the web. The web then passes over guide roll 68 andwinds onto winding roll 70 in preparation for further processing,storage, or shipment to a customer.

In accordance with another embodiment of the present invention, thebacking cylinder roll 46 can be replaced by a backing shoe to provide aneven greater nip width. An example of such an extended nip calenderingarrangement is depicted in FIG. 5. This shoe nip calendering arrangementcomprises a heated calender roll 42, a conformable belt 44 made ofresilient material, and a backing shoe 72. The backing shoe 72 is urgedtoward the heated calender roll 42 by means of loading elements (notshown). During belt operation, the belt 44 glides over the contouredsurface of the backing shoe. To reduce friction during gliding,lubricating oil is supplied between the bottom surface of the belt 44and the curved surface of the backing shoe 72 by an oil lubricationsystem (not shown). The nip width is determined by the width of thebacking shoe, the radius of the heated calender roll, and the thicknessof the belt. A desirable nip width is between about 1 and 25 cm.

Utilizing the apparatus shown in FIG. 3, 4, or 5 with a hot calenderroll surface temperature greater than about 121 deg. C. (250 deg. F.), acalender nipload that varies between about 250 to 500 kN/m and having anip width between about 1 and 25 cm, sample uncoated facestock paperacquired the following density and surface finish characteristics: (1) adensity between about 0.7 and 1.0 g/cc and/or an ash content of lessthan about 15% (measured by the 525° C. standard test method); and (2) afinished surface having a Sheffield smoothness between about 50 and 150Sheffield units (measured in accordance with TAPPI Test Method T 538om-88) and a Parker Print Surf roughness less than about 5.0 microns(measured in accordance with TAPPI Test Method T 555 om-94 using apressure of 10 kgf/cm² and a soft backing (PPS-10).) Additional refiningof the furnish, increased sizing, and/or the application of additionalmechanical calendering, as described herein above, may also contributeto these characteristics depending on, for example, the paper makingequipment that is used.

Referring to FIG. 6, a side view of a laminated adhesive-backed labelproduct 80 utilizing the uncoated facestock paper product 82manufactured by the method described herein above is illustrated. Thelabel product 80 consists of two portions: a lower label portion 81 thatis useful in certain labeling applications (described below); and theentire adhesive-backed label product 80 that is useful in certain otherapplications (described below).

A customer may utilize the uncoated facestock paper product 82 to makethe lower layer portion 81 as follows: (1) apply a coating of releasematerial 86, such as silicone, to a surface of a release liner 88 andallow the release material 86 to dry; (2) apply a coating of adhesive 84over the release material 86 and allow the adhesive 84 to dry; and (3)laminate the release liner 88 to the uncoated facestock 82 so that theadhesive 84 is in contact with the surface opposite the finished surface90 of the uncoated facestock 82. Depending on the type of facestock 82,adhesive layer 84, release material 86, and release liner 88 that areutilized, the resulting product may be used for name badge labels,address labels, shipping labels, desk-top publishing labels, or thelike.

The customer (or a customer downstream to that customer) may utilize theadhesive-backed label described as label 81 to make a waterproof labelas follows: (1) print a pattern (e.g., corporate logo, productdescription, product contents) onto the finished surface 90 of theuncoated paper facestock 82; (2) apply a second adhesive layer 92 to thefinished surface 90 of the uncoated paper facestock 82 (over the printedpattern); and (3) laminate a protective waterproof film 94 to the secondadhesive layer 92. Depending on the type of facestock 82, adhesive layer84, release material 86, release liner 88, second adhesive layer 92, andfilm layer 94 that are utilized, the resulting product may be used fordairy labels, soda container labels, frozen food labels, and the like.

When an uncoated paper product is coated, the resulting ash content willbe driven up considerably. Therefore, a measurement of this parameter isuseful in determining if a facestock material is in fact either coatedor uncoated. An acceptable cutoff percentage for making thisdetermination has been established at 15% as measured by the 525 deg. C.test method (TAPPI Test Method T 211 om-93).

The shoe nip calendering method significantly improves the microscalesmoothness over the macroscale smoothness. That is, where the twoparameters are normally consider by those of ordinary skill in the artto be coupled, they actually become decoupled due to the use of shoe nipcalendering.

Here the term microscale is being used to refer to a scale whereroughness can be characterized by the aforementioned test for ParkerPrint Surf roughness while macroscale refers to a length scale wheresmoothness can be characterized using the aforementioned test forSheffield smoothness. Considering the results of flexographic printingtests, where print quality was based on an absence of print voids, ithas become apparent that printing quality is more dependent on ParkerPrint Surf roughness then on Sheffield smoothness.

The table below lists example trial test data for an uncoated facestockpaper product made in accordance with an embodiment of the presentinvention. EXAMPLE TEST DATA Property Units Sample “A” Sample “B” BasisWeight lb/3,000 sq. ft. 45.9 45.9 Caliper 0.001 inch 3.56 3.59 Densitygram/cc 0.83 0.82 Print Side Smoothness Sheffield Units 75 75 Print SidePPS-10 Microns 3.7 3.9 HST (1%) Seconds 290 230 CD Tensile lbf/inch 2120 MD Stiffness maf 142 CD Stiffness ″ 79

Earlier efforts to create uncoated facestock paper for use in, e.g.,dairy labels, have not been successful as evidenced in the results inthose efforts bearing products with poor flexographic printingproperties, inadequate UV adhesive holdout, and excessive edge wick.Those of ordinary skill in the art should appreciate that the innovativeuncoated facestock paper product disclosed herein overcomes theseproblems resulting in more economical paper facestock products since thefacestock no longer requires to be coated in the conventional manner toacquire those properties. Examples of such conventional coatingprocesses are disclosed in U.S. Pat. Nos. 5,919,524, 5,976,635,5,681,618, and 6,251,477, the contents of which are incorporated byreference herein.

Those of ordinary skill in the art further will appreciated that theexact combination of parameters necessary to produce the uncoatedfacestock product as disclosed herein is difficult at best to providesince there are many variables between different paper making equipment(e.g., equipment type and quality), raw materials, etc. Indeed, the samepaper making machine will perform slightly differently from day to daydue to atmospheric conditions, equipment operating conditions, etc.,requiring periodic equipment adjustments to ensure that all facestockproducts meet their specifications. Therefore, such an exact recipecannot be provided. However, the inventors have provided herein the bestmode known to them and believe the invention is fully enabled so thatone that of ordinary skill in the art of paper making could, withoutunreasonable experimentation, produce the product and perform the methodfound in the claims appended hereto.

While the invention has been described with reference to preferredembodiments, it will be understood by those of ordinary skill in the artthat various changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationto the teachings of the invention without departing from the essentialscope thereof. Therefore it is intended that the invention not belimited to any particular embodiment disclosed as the best modecontemplated for carrying out this invention, but that the inventionwill include all embodiments falling within the scope of the appendedclaims.

1. A paper product, comprising: an uncoated paper facestock including a density between about 0.7 and 1.0 g/cc, and a finished surface having a Sheffield smoothness between about 50 and 150 Sheffield units and a Parker Print Surf roughness (PPS-10) less than about 5.0 microns.
 2. A paper product as recited in claim 1, wherein the uncoated paper facestock further includes an ash content of less than about 15% as measured by the 525° C. standard test method.
 3. A paper product as recited in claim 1, wherein the uncoated paper facestock further includes a 1% HST (80% reflectance) value greater than about 50 seconds.
 4. A paper product as recited in claim 1, wherein the uncoated paper facestock further includes a cross-machine direction tensile strength greater than about 15 lbf/inch.
 5. A paper product as recited in claim 1, wherein the uncoated paper facestock further includes a Gurley Stiffness selected from a group including a stiffness of about 80 and 200 mgf as measured in the machine direction, and a stiffness of about 40 and 200 mgf as measured in the cross-machine direction.
 6. A paper product as recited in claim 1, further comprising a release liner; a release material layer applied on a surface of the release liner to facilitate removal of the release liner from the uncoated paper facestock; and a first adhesive layer applied on the release material layer for adhering the release liner to the uncoated paper facestock, wherein the combined release liner, release material layer, and first adhesive layer are laminated to the surface opposite the finished surface of the uncoated paper facestock.
 7. A paper product as recited in claim 6, further comprising a pattern printed onto the finished surface of the uncoated paper facestock; a second adhesive layer applied on the finished surface of the uncoated paper facestock over the printed pattern; and a film layer laminated to the second adhesive layer.
 8. A paper product, comprising: an uncoated paper facestock including an ash content of less than about 15% as measured by the 525° C. standard test method, and a finished surface having a Sheffield smoothness between about 50 and 150 Sheffield units and a Parker Print Surf roughness (PPS-10) less than about 5.0 microns.
 9. A paper product as recited in claim 8, wherein the uncoated paper facestock further includes a density between about 0.7 and 1.0 g/cc.
 10. A paper product as recited in claim 8, wherein the uncoated paper facestock further includes a 1% HST (80% reflectance) value greater than about 50 seconds.
 11. A paper product as recited in claim 8, wherein the uncoated paper facestock further includes a cross-machine direction tensile strength greater than about 15 lbf/inch.
 12. A paper product as recited in claim 8, wherein the uncoated paper facestock further includes a Gurley Stiffness selected from a group including a stiffness of about 80 and 200 mgf as measured in the machine direction, and a stiffness of about 40 and 200 mgf as measured in the cross-machine direction.
 13. A paper product as recited in claim 8, further comprising a release liner; a release material layer applied on a surface of the release liner to facilitate removal of the release liner from the uncoated paper facestock; and a first adhesive layer applied on the release material layer for adhering the release liner to the uncoated paper facestock, wherein the combined release liner, release material layer, and first adhesive layer are laminated to the surface opposite the finished surface of the uncoated paper facestock.
 14. A paper product as recited in claim 13, further comprising a pattern printed onto the finished surface of the uncoated paper facestock; a second adhesive layer applied on the finished surface of the uncoated paper facestock over the printed pattern; and a film layer laminated to the second adhesive layer.
 15. A method for providing a surface finish on an uncoated paper product having a density between about 0.7 and 1.0 g/cc and a surface with a Sheffield smoothness between about 50 and 150 Sheffield units and a Parker Print Surf roughness (PPS-10) less than about 5.0 microns, the method comprising calendering the uncoated paper product with a hard nip calender.
 16. A method as recited in claim 15, further including the step of calendering the uncoated paper product with an extended nip calender.
 17. A method as recited in claim 16, wherein the step of calendering the uncoated paper product with an extended nip calender includes passing the uncoated paper product through a nip formed between a roller and a soft belt that is pressed against the roller with a shoe.
 18. A method as recited in claim 17, wherein the step of calendering the uncoated paper product with an extended nip calender further includes sufficiently pressing the soft belt against the roller with the shoe to create a nip load between about 250 to 500 kN/m with a nip width between about 1 and 25 cm and heating the roller so that the surface temperature of the roller is greater than about 121° C.
 19. The method as recited in claim 15, further including the step of applying to the paper a sizing agent selected from a group including styrene acrylic acid and styrene acrelate emulsion prior to the step of calendering the uncoated paper product with a hard nip calender.
 20. A method as recited in claim 15, further including the step selected from a group including (a) applying between about 0.5 and 6 g/m² of steam to the surface of the uncoated paper product that is to be finished, and (b) applying between about 0.5 and 6 g/m² of liquid water to the surface of the uncoated paper product that is to be finished. 